1. Field of the Invention
This invention relates to a throttle apparatus which includes an actuator for driving a throttle valve which controls the amount of air. More particularly, to a throttle apparatus which includes a housing in which a ventilation path is provided for being in communication with an accommodation chamber in which a transmission mechanism for transmitting a driving force of the actuator to the throttle valve is accommodated in an external space with each other. The throttle apparatus is provided, for example, in an internal combustion engine.
2. Description of Background Art
An internal combustion engine is known wherein a throttle apparatus which includes a throttle valve includes a driving apparatus which in turn includes an actuator (for example, an electric motor) for driving the throttle valve and a transmission mechanism for transmitting a driving force of the actuator to the throttle valve and a housing which defines an accommodation chamber in which the transmission mechanism is accommodated and the housing has a ventilation path provided therein for being in communication with the accommodation chamber and an external space in which external air which surrounds the housing exists. See, for example, Japanese Patent Laid-Open No. 2007-40216 and Japanese Patent Laid-Open No. 2004-144039.
Where an internal combustion engine which includes a throttle apparatus is incorporated, for example, in a vehicle, the throttle apparatus is surrounded, including a housing thereof, by an external space in which water such as rainwater exists. Therefore, in order to suppress water from intruding into an accommodation chamber through a ventilation path when the housing is splashed with water, while a required ventilation function is assured, the opening area of the ventilation path on the outer face of the housing is reduced or a draining projection is provided on the housing or else the ventilation path is formed as a labyrinth. By the countermeasure, intrusion of water into the accommodation chamber described above is suppressed.
In addition, one of the cases wherein water intrudes into the accommodation chamber through the ventilation path is a case wherein, when the pressure in the accommodation chamber is caused to drop by a temperature change or the like in a state wherein water drops flying to the housing which defines the accommodation chamber or adhering water adhering to the housing and flowing down along the outer face of the housing forms a water film at an outer end opening of the ventilation path (that is, at the opening of the ventilation path on the outer face of the housing) and closes up the outer end opening, the water which closes up the outer end opening is sometimes taken into the accommodation chamber.
With regard to the intrusion of water caused by formation of a water film at the outer end opening of the ventilation path as described above, where the outer end opening of the ventilation path is exposed to the external space, it is difficult to suppress the water film formation at the outer end opening. Further, if the opening area of the outer end opening is reduced in order to suppress intrusion of water into the ventilation path, then a water film becomes likely to be formed at the outer end opening. On the other hand, if the opening area of the outer end opening is increased in order to suppress formation of a water film, then water becomes likely to intrude into the ventilation path from the outer end opening.